Geological modelling for investigating CO2 emissions in Florina Basin, Greece

Abstract

This paper presents an investigation of naturally occurring CO2 emissions from the Florina natural analogue site in Greece. The main objective was to interpret previously collected depth sounding data, convert them into surfaces, and use them as input to develop, for the rst time, 3D geological models of the Florina basin. By also locating the extent of the aquifer, the location of the CO2 source, the location of other natural CO2 accumulations, and the points where CO2 reaches the surface, we were able to assess the potential for CO2 leakage. Geological models provided an estimate of the lithological composition of the Florina Basin and allowed us to determine possible directions of groundwater ow and pathways of CO2 ow throughout the basin. Important modelling parameters included the spatial positions of boundaries, faults, and major stratigraphic units (which were subdivided into layers of cells). We used various functions in Petrel software to rst construct a structural model describing the main rock boundaries. We then de ned a 3D mesh honouring the structural model, and nally we populated each cell in the mesh with geologic properties, such as rock type and relative permeability. According to the models, the thickest deposits are located around Mesochorion village where we estimate that around 1000 m of sediments were deposited above the basement. Initiation of CO2 ow at Florina Basin could have taken place between 6.5 Ma and 1.8 Ma ago. The NESW oriented faults, which acted as uid ow pathways, are still functioning today, allowing for localised leakage at the surface. CO2 leakage may be spatially variable and episodic in rate. The episodicity can be linked to the timing of Almopia volcanic activity in the area.